The present invention relates to liquid injection molding machines and more particularly, the present invention relates to a mold apparatus for a liquid injection molding machine.
Addition curing silicone compositions are well known. Generally, such addition curing silicone compositions comprise the following basic ingredients: a vinyl containing polysiloxane polymer which is preferably vinyl terminated, a hydride polysiloxane cross linking agent and a platinum catalyst. Such compositions may contain vinyl-containing resins or treated silica fillers and specifically treated fumed silica fillers. There also may be present in such compositions vinyl containing fluids. Such compositions may be made containing ordinary hydrocarbon substituent groups or they can be made with fluorosilicone substituent groups which are disclosed in the patents of Jeram, U.S. Pat. No. 4,041,010 and U.S. Pat. No. 4,029,629 which are hereby incorporated by reference. These compositions are normally packaged in two packages such that the vinyl containing polysiloxane is normally packaged with the hydride cross-linking agent or the hydride cross-linking agent is packaged separately with or without the platinum catalyst, that is the platinum catalyst being either with a hydride or with a vinyl containing polysiloxane. Thus, there is no one package which contains both the platinum catalyst, the vinyl siloxane and the hydride cross-linking agent otherwise the composition will cure. Such a composition containing the three ingredients cures at room temperature. It will also cure at elevated temperatures to a silicone elastomer, that is, temperatures above 100.degree. C.
One development in such compositions has been the use of inhibitors. Thus, a methyl vinyl cyclo polysiloxane has been utilized at small concentrations, that is, in parts per million, as an inhibitor. In such compositions, when the composition is mixed together that is when the two packages are mixed together, there is desired a certain amount of shelf life or pot life without the composition curing. However, by heating the composition at elevated temperatures, the cure takes place in a matter of minutes or even seconds. These various inhibitors have been found to have different degrees of potency. Thus, there is the dialkyl maleates inhibitors that are more powerful than methyl vinyl cyclo polysiloxanes and will give a more extended pot life to the composition after the two packages have been mixed, but which will still cure at elevated temperatures in a matter of minutes or even seconds. By elevated temperatures is meant temperatures above 100.degree. C. The use of such dialkyl maleates in addition curing compositions is disclosed in the patent application of R. Eckberg Ser. No. 40,015 which is hereby incorporated by reference.
Another type of inhibitor that can be utilized is isocyanurate inhibitors which are disclosed in Berger and Hardman, U.S. Pat. No. 3,882,083 which is hereby incorporated by reference. An even more important type of inhibitor which can be utilized is the hydroperoxide inhibitors disclosed in U.S. Pat. No. 4,061,609 which is hereby incorporated by reference. The hydroperoxide inhibitor is so potent that it allows the composition to be formed into a single package and such that it has a shelf life of six months or more. The composition can be applied by being heated at elevated temperatures, that is temperatures above 100.degree. C. to cure rapidly to a silicone elastomer, that is in a matter of minutes or even seconds depending upon how high a temperature it is heated. Such addition curing composition, especially with the inhibitor, have new found uses as compositions to be utilized in liquid molding machines. These compositions have all the advantages of the traditional organic plastics and in addition, have the inherent properties of silicones that is the electric insulative properties of silicones, the weathering properties of silicones and specifically their repellency of moisture.
There are two types of traditional liquid injection molding machines that are presently utilized to form molded organic plastics, one is the reciprocating screw type of liquid molding machine and the other type is the ram or plunger type of liquid molding machine.
With respect to the reciprocating screw type of molding machine, such apparatus works by taking the organic pellets and then by the screw thread of the molding machine forcing the pellets by friction force under pressure to melt and form a liquid plastic which is then pressed forward and fed by the screw of the machine into the mold where upon the mold is cooled to cool the plastic to room temperature and form the molded part.
Since the addition curing silicone compositions are liquids in the uncured state and silicone elastomers in the cured state, it is necessary to modify the traditional reciprocating screw molded machine to handle addition curing silicone compositions. The two basic modifications that were made to the reciprocating screw liquid injection molding machine so it could handle liquid compositions, was to provide a shut-off valve to a reciprocating screw plunger from the liquid silicone composition feed tank and also to provide a seal at the end of the reciprocating screw so that liquid composition will not leak out of the reciprocating screw chamber. It was also necessary to heat the mold to cure the silicone composition to a temperature about 100.degree. C.
A disclosure relating to the modification of a reciprocating screw liquid injection molding machine for the handling of liquid silicone compositions and other silicone molding compositions is to be found in the patent application of A. A. Laghi, Ser. No. 159,262 filed on June 13, 1980 and which is hereby incorporated by reference.
The ram or plunger type of liquid injection molding machine was also modified so that it could handle addition curing silicone compositions. Thus, in such apparatus, there was provided a shut-off valve for shutting off the pressure from the feed tank of the liquid silicone composition from the barrel of the plunger injection molding apparatus. There was also provided a seal on the plunger chamber that operates in the plunger chambers so as to prevent a leak of silicone composition. Other necessary modifications were made to accurately control the shot size of a liquid molding composition that was forced by the plunger into the mold to form a molded part as accurately as possible and consistently as possible so that consistently molded parts could be formed without the leaking of molding composition out of the apparatus and without the malfunction of the mold.
The improvements to the plunger type or ram type of molding machine are to be found in the disclosure of A. A. Laghi, Ser. No. 183,620 filed on Sept. 2, 1980 which is hereby incorporated by reference.
Another modification of the liquid injection molding machine was to modify the mold in accordance with the disclosure of A. A. Laghi, Ser. No. 272,242, filed on the same day as the present case and which is hereby incorporated by reference. This patent application which is filed on the same day as the present case disclosures a runnerless mold for forming molded parts. By utilizing a pin which fits exactly into the opening of the nozzle opening through which the liquid silicone composition is forced into the mold cavity, the dripping of liquid silicone composition is prevented out of the nozzle opening of the injection molding apparatus, and accordingly, there is no waste of silicone composition. Further, there are not any runners or cured parts of silicone composition hanging on to the molded part which have to be cut off or removed from the molded part so as to result in the final molded part. Other molding machines or molding apparatuses had drippings or threads hanging on to them which had to be removed before the molded part was ready to be sold and put to its final end use. The drop parts or drip formed portions of the part or threads were unsightly and/or affected the functional operation of the parts in the applications they were intended for.
It should be noted that there is disclosed in the co-pending case of A. A. Laghi that the runnerless molds were known for organic plastics. However, organic plastics are heated to allow them to be injected into the mold and then the mold is cooled to room temperature or below so that the part can be formed and removed from the mold as a finished part. On the other hand, silicone compositions are cooled prior to being injected into the mold and then the mold is heated to cure the material into the molded part. Accordingly, the mechanism for making runnerless molds for organic plastics in liquid injection molding machines could not be applied to molds for forming molded parts from silicone compositions. In addition to the runnerless liquid injection molding apparatus disclosed in the co-pending case of A. A. Laghi, Ser. No. 272,242, it was necessary to devise a means for removing the molded part, once it was formed, from the mold cavity as rapidly as possible and as automatically as possible without detracting from the operation of the mold apparatus. Accordingly, it was desirable to devise a shuttle plate means for removing molded parts from mold apparatus, for forming liquid molding compositions which was heated to cure the silicone part, which removal of the molded part could be done as efficiently as possible and as precisely as possible.
Accordingly, it is one object of the present invention to provide for shuttle plate means for a mold apparatus for a liquid injection molding machine which shuttle plate means is very efficient.
It is another object of the present invention to provide automatic and accurate shuttle plate means for removing molded parts from mold apparatuses for liquid injection molding machines.
It is yet an additional object of the present invention to provide a unique and efficient shuttle plate means for removing parts from mold apparatus for a liquid injection molding machine utilizing silicone compositions which are heated to form the part.
It is still an additional object of the present invention to provide for an efficient and accurate shuttle plate for removing molded parts from the mold cavity in a mold apparatus utilizing a liquid injection molding composition.
It is yet an additional object of the present invention to provide a process for forming molded parts in a mold apparatus for a liquid injection molding machine utilizing addition curing silicone compositions where the shuttle plate means is very efficient and accurate.